This inventor asks you to test it for him. You are given the weapon, and taken to a makeshift firing range behind his workshop. You are instructed to aim down the sites, then pull the lever.
KABOOM!!
The weapon explodes in your hands, damaging you greatly, and killing the over-excited inventor next to you. You now carry a scrap of hot metal in your hands, and the possibilities of such a weapon have died with the inventor you helped.
You loot his workshop for a pittance and move on, never to see another gun, ever.